Study On Corrosion Inhibition Mechanism Of Copper And Copper Alloys By Environment-friendly Corrosion Inhibitors In Salt Solutions

Copper and copper alloys are the most widely used materials due to their excellent properties like mechanical properties,thermal and electrical conductivity,etc.Adding a small amount of organic inhibitors such as cysteine(Cys)is a good choice to improve the corrosion resisting property of copper and its alloys.The corrosion mechanism and cysteine inhibition effect of copper and copper alloys were investigated in the different corrosive medium,i.e.,multiple techniques are used to reveal the composition information of a surface region,and corresponding models revealing the anti-corrosion mechanism are established.The results obtained showed that copper and copper alloys can be corroded in some corrosive media and the corrosion rate can be minimized by using corrosion inhibitors like cysteine(10-2 M).The research work has been classified into three parts and classifications as follows:?.The synergistic inhibitive effect of cysteine and iodide ions on the corrosion behavior of copper was examined in a 0.5 moll-1 Na2SO4 solution(pH=2).Potentiodynamic polarization(PD)curve revealed that Cys acted as a mixed type inhibitor with a major effect on the cathodic process,consequently decreased the corrosion current density to a great extent and shifted the corrosion potential negatively.The investigated results suggested that iodide ions can enhance the inhibition efficiency of Cys.The inhibition mechanism of Cys and the synergistic effect of the two examined reagents were investigated by fitting experimental impedance data according to a projected equivalent circuit for metal/electrolyte interface.The surface analysis further confirmed that the corrosion inhibition was realized due to the adsorption of the inhibitor molecules at the metal/solution interface.Langmuir adsorption isotherm was proposed to describe the inhibition mechanism of Cys on a copper surface.Active sites of Cys molecule were used to form an inhibitor film on the copper surface.The addition of iodide ion increased its inhibition efficiency by enhancing the adsorption of Cys cations through electrostatic interaction with I'pre-adsorbed I ions on the Cu surface.?.The Cys inhibitive effect on Cu-5Zn-5Al-1 Sn alloy in a 3.5 wt.%NaCl solution was examined through a multi approach.Electrochemical results suggested that inhibition efficiency increased with the increase of cysteine concentration.From PD analysis,a decrease in corrosion current and corrosion potential shift toward a more negative direction was observed.The potential difference between the blank and inhibited surface was found to be 46 mV,which is less than 85 mV,revealing a mixed-type inhibition effect of cysteine for the Cu-5Zn-5Al-1Sn alloy.The inhibition mechanism of Cys and the effect of alloying elements were investigated by fitting experimental impedance data according to a projected equivalent circuit for the alloy/electrolyte interface.A Langmuir adsorption isotherm was proposed to explain the inhibition phenomenon of cysteine on the Cu-5Zn-5Al-1Sn alloy surface.Surface morphology observation confirmed that the Cu-5Zn-5Al-1 Sn alloy was attacked in 3.5 wt.%NaCl solution and could be inhibited by using the cysteine inhibitor.The impact of alloying elements on the corrosion mechanism was further examined by surface analysis techniques such as X-Ray photoelectron spectroscopy(XPS)/Auger spectra,the results of which indicated that the corrosion inhibition was realized by the adsorption of the inhibitor molecules at the alloy/solution interface.?.Based on the work of the second part,the effect of immersion time on the corrosion behavior of Cu-5Zn-5AI-1Sn alloy with the addition of cysteine in 3.5 wt.%NaCl solution has been further studied using electrochemical and surface analysis techniques.The results of PD and electrochemical impedance spectroscopy(EIS)showed that Cu-5Zn-5Al-1Sn alloy can be corroded in 3.5 wt.%NaCl solution and the corrosion effect increased with immersion time.The increase in corrosion rate resulted from the degradation of the alloy surface through the immersion period.Cysteine can act as an anti-corrosion substance as examined by inhibition efficiency calculated from PD and EIS results.On the other hand,scanning electron microscopy(SEM)morphological test clarified that the damage on the alloy surface has been reduced on the addition of cysteine.The presence of S and N species in the electron dispersion spectroscopy(EDS)analysis provides further information on the presence of cysteine on the alloy surface.Raman and XPS analysis further strengthen the results by giving other critical parameters such as the oxidation state of each element on the surface hence determining the surface reaction.In this regard,the surface contribution of the alloying constituent is copper atom forming an inhibitor film to protect the alloy from further degradation.Other constituent metals are bounded by the formed inhibitor film.An adequate adsorption isotherm and inhibition mechanism are suggested using PD and EIS results and Langmuir adsorption isotherm has been chosen to describe surface phenomena of Cu-5Zn-5Al-1Sn alloy in 3.5 wt.%NaCl solution for entire immersion period.